Conversion of a video signal for driving a liquid crystal display

ABSTRACT

Method and apparatus for the conversion or generation of a video signal intended to be displayed on an image display with different luminance response times for rise and decay. The conversion or generation of the video signal is so that motion artifacts which are caused by the difference in luminance response times for rise and decay such as large area luminance jumps, large-area flicker and faulty temporary large-area luminance are fundamentally cancelled in the displayed image.

This appln is a continuation of PCT/EP99/02060 filed Apr. 17, 1998.

FIELD OF THE INVENTION

The present invention relates to the display of images on image displayswith different luminance rise and fall response times, such as liquidcrystal displays, in particular to the display of TV pictures and/ordata information on a video display system equipped with a liquidcrystal display device.

BACKGROUND AND DESCRIPTION OF RELATED ART

The display of video images on display devices such as a Cathode RayTube (CRT) or a Liquid Crystal Display (LCD) is a known art. Imagedisplays equipped with such CRT or LCD display devices are capable ofdisplaying on a display screen images consisting of a number of pictureelements (or pixels) which are refreshed at a refresh rate generallyabove 25 Hz. These images may be monochromatic, multicolour orfull-colour. Common standards are in use to display the images as asuccession of frames.

The light of the successive frames which are displayed on the displayscreen of such a CRT or LCD display device is integrated by the humaneye. If the number of displayed frames per second—further called theframe rate—is sufficiently high, an illusion of the images beingdisplayed in a continuous way, and therefore an illusion of motion, canbe created.

The way images are formed on the display screen of a CRT display deviceis fundamentally different from the way images are formed on the displayscreen of a LCD display device.

On a CRT display device, the luminance of a picture element is producedby an area of a phosphor layer in the display screen when said area ishit by a writing electron beam.

On a LCD display device, the luminance of a picture element isdetermined by the light transmittance state of one or more liquidcrystal elements in the display screen of the LCD display device at thelocation of the picture element, whereby the light itself originatesfrom ambient light or a light source.

For a faithful reproduction of moving images or moving parts of animage, the luminance response of the display device being used is ofutmost importance.

The luminance responses and the luminance response times of displayscreens are known to be very different for CRT and LCD display devices.The luminance response time, being the time needed to reach the correctluminance on the display screen in response to an immediate change in acorresponding drive signal is shorter than a frame period for a CRTdisplay device but up to several frame periods for a typical LCD displaydevice according to the state of the art.

For LCD display devices, the luminance responses and luminance responsetimes are also known to be different for a darker-to-brighter luminancetransition as compared to the responses and response times for a similarbrighter-to-darker luminance transition. Furthermore, the luminanceresponses and luminance response times are temperature dependent, drivevoltage range dependent and, due to production tolerances, unequal overthe LCD screen area (location dependent).

Various solutions are known for changing luminance response times withLCD display devices. They however have the aim to shorten the overallluminance response times, not to make the luminance rise and fall timesequal. EP 0 487 140 discloses a method for speeding up display responsetimes by doubling the display frame rate. The luminance rise and falltimes remain different. EP 0 553 865 describes luminance flickerphenomena related to luminance response, but these phenomena are not dueto the difference between luminance rise and fall times, but rather tohow image lines are written.

There exist a number of images, further referred to as specific images,which when moved over a display screen with different luminance rise andfall times, give rise to visible and measurable artefacts in thedisplayed image, even when the luminance responses are shortened.

It is characteristic of such specific images that they contain a numberof isolated or clustered picture points, which are in high contrast totheir surroundings in the image.

The artefacts are due to the difference between luminance rise and falltimes, which is typical for an LCD display device. This causes theluminance fall (or rise) of a white spot at a first location to bedifferent from the simultaneous luminance rise (or fall) of a white spotat a second location, when the white spot is moved from the first to thesecond location. The total luminance integrated over the screen areaimmediately before, during and after the movement of the white point isnot constant. The integrated luminance shows a ‘luminance jump’.

In practice, the artefacts will only be visible when more pictureelements change luminance at the same time within the observation fieldof the viewer.

In practice, various different artefacts may appear dependent on variousparameters such as the difference between luminance rise and fall times,the frame rate of the displayed image, the video signal levels, thespeed with which the image is moved over the screen, the image content.

The visible artefacts cause the quality of the displayed image to rangefrom being inferior to unacceptable. The known solutions of increasingthe frame rate do not fundamentally solve the problems but only makethem in the best case less perceptible.

SUMMARY OF THE INVENTION

It is the aim of this present invention to remove luminance jumps andvisible artefacts resulting from said luminance jumps in a displayedimage during and immediately after the movement of the image, theluminance jumps and the artefacts caused by a difference in luminancerise and fall times of the display screen on which the image isdisplayed.

This is obtained by a method for converting a first video signal into asecond video signal, the second video signal being intended for beingdisplayed on a display device with different luminance rise and falltimes, which comprises a display screen, and which operates at a frameperiod. The conversion is so that the second video signal causes theluminance time response of a picture element of the image to a change ofthe first video signal from a first amplitude value to a secondamplitude value to be substantially equal in shape and amplitude butreversed (i.e., inverted) in slope compared to the luminance timeresponse of the same or another picture element of the image to a changeof the first video signal from the second amplitude value to the firstamplitude value. The luminance time responses can be made substantiallyequal to ‘predefined luminance time responses’.

The luminance time responses can be made substantially equal inamplitude and not slower than the luminance response of the same oranother picture element which would be caused by the first video signalif this were displayed without conversion. The choice of the same oranother picture element can be the same picture element itself, areference picture element from a selected group of picture elements(e.g. a window) to which the same picture element belongs, any pictureelement which can be displayed on the display screen of the displaydevice. The chosen same or another picture element can be that pictureelement of all picture elements which are aimed to be displayed of whichthe luminance response is the slowest. The conversion permits thecompensation of the unevenness of the luminance rise and fall times overthe surface of the display screen, as well as the compensation of thetemperature dependency of the luminance rise and fall times.

According to a preferred embodiment, the conversion is such that thesecond video signal is built up in real time in consecutive steps duringcorresponding consecutive correction periods.

For the determination of a next step, one or more of the followingparameters may be taken into account at the start of a correctionperiod:

the present luminance of the picture element as predicted at the instantof the previous correction period,

the present amplitude of the first video signal,

the physical location of the picture element on the display screen,

the present temperature at the location of the picture element.

Preferably, a correction period is equal to a multiple of the frameperiod of the second video signal.

Preferably, the frame rate of the second video signal is a multiple ofthe frame rate of the first video signal.

According to an embodiment of the present invention, the conversion ofthe first video signal into the second video signal is so that thefaster luminance response of a picture element to a change of the firstvideo signal is slowed down in order to match the luminance response intime and amplitude to the known slower luminance response of the same oranother picture element for the opposite change of the first videosignal.

According to another embodiment of the present invention, the conversionof the first video signal to the second video signal is so that theslower luminance response of a picture element to a change of the firstvideo signal is accelerated in order to match the luminance response intime and amplitude to the known faster luminance response of the same oranother picture element for the opposite change of the first videosignal.

According to another embodiment of the present invention, the conversionof the first video signal to the second video signal is so that thesecond video signal causes the luminance time response of a pictureelement to a change of the first video signal from a first amplitudevalue to a second amplitude value to be substantially equal in shape andamplitude but inverted in slope compared to the luminance time responseof the same or another picture element for a change of the first videosignal from the second amplitude value to the said first amplitudelevel, the luminance responses being equal to predefined luminanceresponses.

Furthermore, an apparatus is disclosed and claimed for carrying out amethod as described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1a, FIG. 1b and FIG. 1c illustrate the display of a specific videosignal and its scrolling down over the display screen;

FIG. 2 illustrates the display of a specific “text window” video signaland its movement over the display screen;

FIG. 3a, FIG. 3b, and FIG. 3c illustrate the movement of a white pointbetween a first location and a second location on a display screen;

FIG. 4 shows luminance responses on a display screen of which theluminance rise time is shorter than the luminance fall time, when awhite point moves from a first to a second location (prior art);

FIG. 5 shows luminance responses on a display screen of which theluminance rise time is longer than the luminance fall time, when a whitepoint moves from a first to a second location (prior art);

FIG. 6a, FIG. 6b, and FIG. 6c illustrate a horizontal movement of twowhite points on a display screen;

FIG. 7a, FIG. 7b, FIG. 7c illustrate a horizontal movement of threewhite points on a display screen;

FIG. 8a, FIG. 8b, and FIG. 8c illustrate a vertical movement of twowhite points on a display screen;

FIG. 9a, FIG. 9b, and FIG. 9c illustrate a movement of a cluster ofwhite points on a display screen;

FIG. 10 illustrates a movement in three steps of a white point on adisplay screen;

FIG. 11 shows a luminance response on a display screen of which theluminance rise time is longer than the luminance fall time, when a whitepoint moves on the display screen during three consecutive frame periods(prior art);

FIG. 12 shows a prior art connection of a video generator to an imagedisplay;

FIG. 13 is a block diagram of an embodiment of the present invention;

FIG. 14a shows a waveform of a first video signal corresponding to animage point which changes first from black to white and later from whiteto black;

FIG. 14b shows a waveform of a prior art RMS drive voltage to anindividual liquid crystal cell in a LCD display screen to let it changeluminance first from black to white and later from white to black;

FIG. 15a shows the luminance response of a picture element on a LCDdisplay screen of which the luminance rise time is shorter than theluminance fall time, according to the present invention and compared toprior art;

FIG. 15b shows a waveform according to the present invention of a RMSdrive voltage to an individual crystal cell in a LCD display screen tolet it change luminance first from black to white and later from whiteto black;

FIG. 15c shows a waveform according to the invention of a second videosignal corresponding to a picture element which changes first from blackto white and later from white to black;

FIG. 16 shows how a luminance response is controlled according to theinvention;

FIG. 17a shows the luminance response of a picture element on a LCDdisplay screen of which the luminance rise time is longer than theluminance fall time, according to the present invention and compared toprior art;

FIG. 17b shows a waveform according to the present invention of a RMSdrive voltage to an individual crystal cell in a LCD display screen tolet it change luminance first from black to white and later from whiteto black;

FIG. 17c shows a waveform according to the present invention of a secondvideo signal corresponding to a picture element which changes first fromblack to white and later from white to black;

FIG. 18 shows a stand-alone apparatus according to the presentinvention;

FIG. 19 shows an apparatus according to the present invention, connectedbetween a video generator and an image display;

FIG. 20 shows a video generator with a built-in apparatus according tothe present invention, which is connected to an image display; and

FIG. 21 shows a video generator which is connected to an image displaywhich contains an apparatus according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

A first example of a specific image is illustrated in FIG. 1a, FIG. 1band FIG. 1c. An image display 1 has on its display screen 2 a specificimage 3 characterised by a high noise content, the image being scrollingdown at such a slow speed that the scrolling steps are individuallyperceptible. FIG. 1b shows an enlarged part 4 of the specific image 3,its location referred to the image being shown in FIG. 1a, FIG. 1b andFIG. 1c illustrate a downward scrolling step equal to the differencebetween the distance 5 of a bright image point 6 to the top border ofthe image before a scrolling step and the distance 7 after the scrollingstep.

A second example of a specific image is illustrated in FIG. 2 and showsa window 8 with text inside, which is moved over a display screen 2 froma location 9 to a location 10. Depending on the luminance rise and fallresponses of the display device and on the scrolling or movement speed,artefacts are seen as a large-area luminance flash, large-area luminanceflicker, a temporary faulty large-area luminance.

FIG. 3a, FIG. 3b and FIG. 3c illustrate the movement on a display screenof a white point 11 with the dimension of a picture element rom a firstposition 12 (FIG. 3a) to a second position 13 (FIG. 3 c). Only a smallpart 14 of the display screen enclosing the two locations 12 and 13 isshown in an enlarged way.

When the white point changes instantly from the first position 12 to thesecond fposition 13, the following happens.

On a display screen of which the luminance response is immediate, thewhite point will at the same instant fully disappear at the firstlocation 12 and fully reappear at the second location 13; the luminanceintegrated over the screen area 14 at time instances before, during andafter the move of the white point will be equal to the luminancecorresponding to one white point.

On a display screen with a luminance rise time different compared to theluminance fall time as it is typical for an LCD display device, theluminance fall (or rise) of the white spot at the first location 12 willbe different from the simultaneous luminance rise (or fall) of the whitespot at the same instant at the second location 13; the total luminanceintegrated over the screen area 14 is not equal immediately before,during and after the movement of the white point.

In FIG. 4 is shown the luminance before, during and after the movementof the white point 11 at a time instant T0 from a first location 12 to asecond location 13 on a display screen of which the luminance rise timeis shorter than the luminance fall time. The horizontal axis 15 is atime scale and the vertical axis 16 is a luminance scale. Graph 17 showsthe luminance of the picture element at the first location 12, graph 18shows the luminance of the screen picture element at the second location13, and graph 19 shows the integrated luminance over the screen area 14.

In FIG. 5 is shown the luminance before, during and after the move ofthe white point 11 at a time instant T0 from a first position 12 to asecond position 13 on a display screen of which the luminance rise timeis longer than the luminance fall time. Graph 20 shows the luminance ofthe picture element at the first location 12, graph 21 shows luminanceof the picture element at the second location 13, and graph 22 shows theintegrated luminance over the screen area 14.

FIG. 4 and FIG. 5 show that when the white point 11 moves from the firstposition 12 to the second position 13, there is a short luminance jump,upwards or downwards depending on how the rise and fall times of thedisplay screen relate to each other. Within a same time period, theluminance of the picture element at the second location 13 is changeddifferently compared to the luminance of the picture element at thefirst location 12, the difference determining the amplitude of theluminance jump. This luminance jump is at the origin of the artefactsmentioned above and further explained below.

If more white points are moved at the same instant and within the samesmall area of the display screen, a luminance jump will occur as wellbut its amplitude depends on how the white points are distributed withinthe same area.

FIG. 6a, FIG. 6b and FIG. 6c illustrate how two white points layingside-by-side move in the same horizontal direction over a distance ofone picture element. In FIG. 6b is shown that one picture element doesnot change luminance, while two other picture elements change luminance.Compared to the move of one white point as described above, theamplitude of the luminance jump within the area 14 is equal, however therelative luminance jump being the absolute luminance jump related to thetotal luminance of the moving points is smaller.

FIG. 7a, FIG. 7b and FIG. 7c illustrate how three white points layingside-by-side move in the same horizontal direction over a distance ofone picture element. In FIG. 7b is shown that two picture elements donot change luminance, while two other picture elements change luminance.Compared to the move of one white point as described above, theamplitude of the luminance jump within the area 14 is equal. Compared tothe move of two white points as described above, the amplitude of theluminance jump within the area 14 is equal, however the relativeluminance jump being the absolute luminance jump related to the totalluminance of the moving points is smaller.

FIG. 8a, FIG. 8b and FIG. 8c illustrate how two white points above eachother move in the same vertical direction over a distance of one pictureelement. FIG. 8b shows that four picture elements do change luminance atthe same time. Compared to the move of one white point, the luminancejump is doubled, but the relative luminance jump is the same.

Different combinations of white points moving at the same time in a samedirection from one first location to a second location within an area ofthe image screen will give different absolute and relative luminancejumps within said area. FIG. 9a, FIG. 9b and FIG. 9c illustrate amovement of a larger combination or cluster of white points from onelocation to a more right-down location.

FIG. 10 illustrates a white point 11 moving during a time interval T0-T3of 3 frame periods from location 23 to location 26 over locations 24 and25, within a screen area 14. FIG. 11 shows the luminance graph 27 infunction of time, integrated over the area 14. A temporary lowerluminance 28 occurs during the move of the white point. The luminance istemporarily faulty. This artefact is related to the image jump andfurther mentioned as a ‘temporary faulty luminance’.

The ‘luminance jump’ and ‘temporary faulty luminance’ artefacts wereexplained hereabove for simple moving images composed of one or morewhite points. These artefacts however occur more or less visible and/ormeasurable with any image moved on a display screen of an image devicewith different luminance rise and fall times. When an above mentionedspecific image, for example the image illustrated by means of FIG. 1a,is moved over the screen whereby its content remains unchanged,depending on the speed of the movement, artefacts ranging from aluminance jump (or a brighter or darker luminance flash), over alarge-area flicker to a large-area faulty luminance may occur. Theartefacts occur only in the images or in parts of the image which aremoved.

In FIG. 12 is shown a prior art connection 31 of a video generator 29 toan image display 1 which has a screen 30.

An embodiment of the present invention is explained by means of blockdiagram FIG. 13 and figures of waveforms. It is an apparatus in which afirst video signal is converted into a second video signal.

FIG. 13 shows a block diagram of 32 (specifically, a video signalconverter) according to the present invention. The input is a firstvideo signal 33, and the output is a second video signal 34 which is aconversion of the first video signal 33. The apparatus 32 comprisesseveral functional blocks, being an optional inverse gamma correction35, a subtractor 36, a first adder 37, a second adder 38, a processingblock 39, a one-frame memory FM, and an optional gamma-correction 40.The functional blocks are interconnected through severalinterconnections for the interchange of values between the functionalblocks. These values may correspond to luminances, or to gamma-correctedvideo signals, or to video signals without gamma-correction, or to acombination of one or more of these, depending on where the apparatus 32is located in a video chain between a video generator and a displaydevice. For the description of the apparatus 32, it is assumed that thevalues are linearly related to luminances on the display screen and thatthe first and second video signals are not gamma-corrected. It willhowever be easy to extend the apparatus for gamma-corrected videosignals by the addition of an inverse gamma-correction 35 at the inputside, and a gamma-correction 40 at the output side, or by integratinggamma-awareness into the apparatus 32.

The processing block 39 has an optional input for values TL, thesevalues being related to the present status of a picture element of thedisplay screen such as temperature, location of the picture elementbeing processed, differences in display behaviour between productionbatches, ageing of the display, intended to be used for compensations inthe conversion of the first video signal into the second video signal.These values may come from a sensor in the display device, or beuser-configurable through an on-screen display or an external data entrydevice.

For the explanation of the operation of the apparatus 32 of FIG. 13,FIG. 14a shows a chosen first video signal IN1. This chosen first videosignal corresponds to a white picture element on a black background, thewhite picture element appearing at time T0 and disappearing at time T10.In FIG. 14a, the horizontal axis is a linear time scale with divisionsTF1 corresponding to frame periods of the first video signal, and thevertical axis is a linear voltage scale. The first video signalamplitude changes at T0 from I0 to I1, and at T10 from I1 to I0.

FIG. 14b shows the waveform of the RMS drive voltage applied inside atypical LCD display device to the one or more liquid crystal imagecell(s) of the display screen of LCD display device which are driven todisplay the white point of the first video signal IN1, this beingaccording to prior art.

FIG. 15a shows a number of luminance time responses of a picture elementon a display screen of an LCD display device of which the luminance risetime is shorter than the luminance fall time. The horizontal axis is alinear time scale, and the vertical axis 41 is a linear luminance scale.The luminance responses in FIG. 15a correspond to one unique LCD displaydevice; the response is dependent on the display device, the location ofthe picture element on the display screen, and on the temperature.

Graph 42 on FIG. 15a shows the prior art luminance response to the firstvideo signal IN1 at the location of the displayed picture element. Asshown, the luminance rises from time instant T0 for a duration ofseveral frame periods from L0 to L1, and falls from time instant T10 fora duration of several frame periods. The luminance rise time is shorterthan the luminance fall time.

Graph 43 shows the prior art luminance response of the same pictureelement to a first video signal which is reversed in amplitude comparedto video signal IN1 and which is further called −IN1. Luminance rise andfall times are as with Graph 42.

Video signals IN1 and −IN1 do not occur at the same instant for drivingthe same picture element, but may both be present at the input within atime interval shorter than an input frame period when e.g. a whitepicture element moves from one location to another within the image.

According to the present invention, the luminance rise and fall timesare made equal, obtained by slowing down the faster response to matchwith the slower response, or accelerate the slower response to matchwith the faster response, or make the faster and the slower responseequal to a predefined luminance response, the three methods beingpossible with the here described embodiment. Accelerating the slowerresponse will however not always be useable in practice because higherdrive voltages will be needed and saturation may occur in the imagedisplay.

The solution is only fully explained for making the faster responseslower. Making the slower response faster, or making the faster responseand the slower response equal to predefined responses, can easily beimplemented by the skilled person.

In accordance with the present invention, graph 42 in FIG. 15a is sloweddown to graph 44 during the time interval of rising luminance andmatches as close as possible to graph 45 being the inverse of thefalling graph 43. During the interval of falling luminance (from T10on), the response should not be modified but should remain as graph 42.

FIG. 16 is an enlarged version of a part of FIG. 15a, namely betweentime instances T0 and T3. To the first vertical axis 41 is added asecond vertical axis 46 in order to show the relation between the secondvideo signal and the luminance of the image on the display screen.

The method for converting or modifying the first video signal to developthe second video is further explained referring to the block diagramFIG. 13.

The conversion is such that the second video signal is built up in realtime in consecutive steps during corresponding consecutive correctionperiods TC. A correction period (TC) is by preference equal to the frameperiod of the displayed image. A correction period may be different fromthe frame period (TF1) of the first video signal.

From the present value of the first video signal 33 is subtracted in thesubtractor 36 a value FR which corresponds to the present luminance asit was predicted one correction period before. The result is a value Δ.The value Δ determines how the luminance will have to change during thenext correction period. Luminance should increase or rise when Δ ispositive, decrease or fall when Δ is negative, and remain equal when Δis zero. The value Δ is applied to a first input of the processing block39. At a second input is applied the predicted present luminance FR.With as input values Δ and FR and if present the input of one or moretemperature values TL related to the connected display screen, aredetermined two output values, ΔC and ΔR. How these values ΔC and ΔR canbe determined is explained further. ΔC is a correction value to be addedto the predicted present luminance FR in order to reach a chosenluminance (to match to a chosen response) at the end of the nextcorrection period. ΔR is the value with which the luminance will havechanged after the next correction period when ΔC is added to thepredicted present luminance FR taking into account the parameters of thedisplay screen (of which some are screen-location, voltage andtemperature dependent).

The value ΔC is added in the first adder block 37 to the predictedpresent luminance FR. The predicted present luminance FR was predictedat the beginning of the previous correction period and has been delayedover one correction period in a one-correction-period storage element ormemory FM. The output of the first adder 37 is a value which is thesecond video signal 34 without optional gamma-correction.

The value ΔR is added in the second adder block 38 to the value of thepredicted present luminance FR. The output is the predicted presentluminance for a next correction period.

Although a correction to the second video signal takes severalcorrection periods, a memory FM of only one correction period (or onlyone second video signal frame period) is needed. For each correctionperiod a new correction value is determined based on the presentluminance which was calculated at the start of the previous correctionperiod and stored during one correction period.

The above described apparatus 32 contains all the above mentionedfunctional blocks and connections to change a luminance response inconsecutive steps by converting the first video signal 33 to the secondvideo signal 34. It is however not always needed to change the luminanceresponse, namely when the luminance response already follows the slowestresponse with the first video signal, the apparatus can worktransparently. This can be realised in the processing block 39.

For further explanation reference is made now to FIG. 16 in which isshown how the luminance response is built up during three consecutivecorrection periods from the time instances T0 to T3.

From T0 to T1, without correction, the luminance rise would follow graph42 and increase from LF to LA1. According to the invention, theluminance response should however follow graph 45 and increase from LFto LB1. The shape of the rising luminance slope is however not exactlyidentical to the opposite of the shape of the falling luminance slope,and so it is difficult to match the rising luminance to the graph 45 andat the same time reach luminance LB1 at time instant T1. More importantis however that the integrated luminance over the correction period fromT0 to T1 is correct. Therefor, the luminance should raise so that theintegrated luminance is the same as it would be if graph 45 werefollowed and LB1 reached at T1. This is so when the luminance followsthe exponential graph 47, whereby the luminance is LD1 at T1. Thecorrected luminance response is marked as 44 on FIG. 16 (and FIG. 15a).Referring to FIG. 13 and its explanation, ΔC should have an appropriatevalue to correct the second video signal so that the luminance increasesto LC1 over a number of correction periods; LD1 is the predicted presentluminance FR at the end of the correction period T0-T1.

At T1, a following correction period T1-T2 starts. The luminance shouldcontinue to follow as closely as possible graph 45 and at the same time,the integrated luminance over T1-T2 should be [equal] substantially thesame as if the luminance response did follow graph 45. Therefore, theluminance should rise (graph 48) to the luminance LC2 and rise from LD1to LD2 within the correction period T1-T2. LD2 is the predicted presentluminance after the correction T1-T2. If the video signal would not havebeen corrected, a luminance LA2 would have been reached at T2.

On the vertical axis 46 in FIG. 16 values are set out with reference toFIG. 13 and its explanation. The first video signal amplitude value goesfrom INF to INT at T0. At T1, the difference between the value of thefirst video signal and the predicted present luminance FR predicted atT0, is Δ1=INT−FR1. The output of the processing block is ΔC1 and isadded to FR1 to be the new second video signal value. The predicted riseof luminance after the correction period T1-T2 is ΔR1, and the predictedpresent luminance at T2 is FR1+ΔR1=FR2. From T2 on, the luminanceresponse is built up in the same way as described here before up toluminance LT. On FIG. 15a is shown, that from T10, the luminanceresponse follows the slower luminance falling response and no correctionis carried out, the apparatus 32 working transparently.

FIG. 15b shows the waveform of the RMS drive voltage with reference toFIG. 14b, but now in response to the second video signal.

FIG. 15c shows the second video signal, being the converted first videosignal shown in FIG. 14a.

In FIG. 17a, FIG. 17b and FIG. 17c are shown similar waveforms comparedto FIG. 15a, FIG. 15b and FIG. 15c, however for a display device ofwhich the luminance rise time is longer than the luminance fall time.The luminance fall is now made slower from T10.

In the processing block 39 of FIG. 13, the output values ΔC and ΔR aredetermined as a function of the input values Δ and FR and optionaltemperature values and location values. The following C-languagefunction is hereby used.

-------------------------------------------------------------------------------------void calc_deltas(int delta_in, int from, int *delta_out, int *delta_res){  float dout, dres;  if (delta_in > 0) /* positive slope */  {   /* nodrive correction needed */   dout = delta_in;  }  else       /* negativeslope */  {   /* correction value */   dout = (float)delta_in *       (  (FRAME_PERIOD - tau_rising*(1 - exp(-FRAME_PERIOD/tau_rising)))        / (FRAME_PERIOD - tau_falling*(1 -exp(- FRAME_PERIOD/tau_falling)))       )      *temp_function(temperature, FALLING)      *location_function(screen_x, screen_y);  }   /*    * Predict pixelresponse. To be used in next frame iteration.    * Always predict theslowest edge, since that is what we want to    * make the fastest one doas well .    */  dres = (float)delta_in       * (1 -exp(-FRAME_PERIOD/tau_rising))       * temp_function(temperature,RISING)       * location_function(screen_x, screen_y);  *delta_out =(int)rint(dout);  *delta_res = (int)rint(dres); }-------------------------------------------------------------------------------------

In the above shown C-language function, corrections are determined every{fraction (1/60)} second (frame rate 60 Hz). It is written for thedisplay of an image on a display device of which the luminance rise timeis longer than the luminance fall time. Values “delta_out” (being ΔC)and “dres” (being ΔR) are calculated from “delta_in” (being Δ) and“from” (being FR). When “delta_in” is positive, the luminance shouldrise (called positive slope) and no correction is to be made. Thecalculation of dout (or ΔC) is based on the following equation wherein Tis the correction period:${\Delta \quad C} = {\Delta \cdot \frac{T - {\tau_{S}\quad \cdot \left( {1 - ^{\frac{- T}{\tau_{S}\quad}}} \right)}}{T - {\tau_{F}\quad \cdot \left( {1 - ^{\frac{- T}{\tau_{F}\quad}}} \right)}}}$

The calculation of “dres” (ΔR) is based on the following equation:${\Delta \quad C} = {\Delta \cdot \left( {1 - ^{\frac{- T}{\tau_{S}\quad}}} \right)}$

τ_(S) (or tau_rising) and τ_(F) (or tau_falling) are time constants ofexponential functions corresponding to luminance time responses.

The C-program function includes a correction in function of temperature(temp_function) and location (location_function).

The processing block 39 may be implemented in different ways. It may bea pre-calculated look-up table with Δ and FR as input values, and ΔC andΔR as output values which before being output are sent throughmultipliers for temperature and location dependent corrections.

It may be a hardware implementation of the C-program function shownabove.

It may consist of a look-up table and a microprocessor to update thevalues in the look-up table in function of temperature.

FIG. 18, FIG. 19, FIG. 20 and FIG. 21 show other possible embodiments orapplications of the present invention. FIG. 18 shows a stand-aloneapparatus 49 which according to the present invention converts a firstvideo signal 33 into a second video signal 34, having an optional input50 for values (TL) related to a display screen and having an optionaltemperature sensor 51 for measuring a temperature of a display screen.FIG. 19 shows according to the invention an apparatus 52 whichcorresponds to apparatus 32 of FIG. 13 and is connected between a videogenerator 29 and an image display 1. FIG. 20 shows according to thepresent invention an apparatus 52 built-in inside a signal generator 29which is connected to an image display 1. FIG. 21 shows according to thepresent invention an apparatus 52 built-in inside an image display whichis connected to a video generator 29.

It is also a possible application of the present invention that a videosignal is generated or converted inside a signal generator so that theluminance time responses of a picture element of an image, displayed ona display device with different luminance rise and fall times, are equalfor an amplitude change of the video signal and for the oppositeamplitude change of the video signal.

What is claimed is:
 1. An apparatus (32) for converting a first videosignal (33) into a second video signal (34), characterised in that itcomprises: a subtractor (36) for subtracting from the first video signal(33) a predicted present luminance, a processing block (39), having asinput the output of the subtractor and the predicted present luminance,and as output a first and a second correction value, a first adder (37)for adding the first correction value of the processing block (39) andthe predicted present luminance, thus forming the second video signal(34), a second adder for adding the second correction value and thepredicted present luminance, thus forming the next predicted presentluminance, a one-frame memory, for delaying the next predicted presentluminance, thus forming the predicted present luminance for a nextcorrection period.
 2. A method for operating a display device,comprising: substantially equalizing luminance rise and fall responsesof elements in a screen of said display device in time with slopes ofthe substantially equalized rise and fall responses being invertedrelative to one another, said display device being prone to displayartefacts including luminance jumps due at least partially todifferences between said luminance rise and fall responses, includingmodifying a first video signal, which has video information, from timeto time in accordance with a predetermined schedule based at least oncharacteristics of said elements in the screen to develop a second videosignal having said video information, and feeding said second videosignal to said display device.
 3. A method as in claim 2 wherein saidmodifying includes developing the second video signal to cause theluminance time responses to be substantially equal to predeterminedluminance time responses.
 4. A method as in claim 2 or 3 wherein saidmodifying includes developing said second video signal as fed to saiddisplay device to substantially equalize said luminance rise and fallresponse in shape, amplitude and slope.
 5. A method as in claim 2 or 3wherein said modifying includes developing said second video signal inconsecutive steps during corresponding consecutive correction periods.6. A method as in claim 5 including taking into account at the start ofa correction period, for the determination of the next correctionperiod, at least one of the following parameters: a) the presentluminance of the picture element as predicted at the instant of theprevious correction period; b) the present amplitude of the first videosignal; c) the physical location of the picture element on the displayscreen; and d) the present temperature at the location of the pictureelement.
 7. A method as in claim 5 including selecting a correctionperiod equal to a multiple of a frame period of the said first videosignal.
 8. A method as in claim 2 or 3 wherein said modifying includescausing the second video signal to effect a luminance response of apicture element of said screen to be one of slowed down and acceleratedin order to match the luminance response in time and amplitude to aknown corresponding slower or faster luminance response of a same oranother picture element for the opposite change of the first videosignal.
 9. A method as in claim 2 or 3 including selecting a frame ratefor the second video signal to be different from the frame rate of thefirst video signal.
 10. A display system comprising: a display devicehaving a screen which is prone to display artefacts including luminancejumps due at least partially to differences between luminance rise anddecay responses of elements in said screen; means for modifying a firstvideo signal from time to time in accordance with a predeterminedschedule based at least on characteristics of said elements in thescreen to develop a second video signal, and means for feeding saidsecond video signal to said display device for substantially equalizingsaid luminance rise and fall responses in time with slopes of the riseand fall responses being inverted relative to one another.
 11. A displaysystem as in claim 10 wherein a value of said second video signal thatcorresponds to a predetermined pixel has from said time to time astepwise formation.
 12. A display system as in claim 10 or 11 whereinsaid means for modifying a first video signal includes: processing meansconnected between an input which receives said first video signal and anoutput which provides said second video signal for feeding to saiddisplay device, and memory means connected to said processing means forholding for a given correction period a signal corresponding to apredicted present luminance for use in a next correction period.
 13. Adisplay system as in claim 10 wherein said display device includes aliquid crystal display device.
 14. A display system as in claim 10wherein a frame rate of the second video signal is different from aframe rate of the first video signal.
 15. A display system as in claim10 wherein said means for modifying a first video signal causes thesecond video signal to effect a luminance response of a picture elementof said screen to be one of slowed down and accelerated in order tomatch the luminance in time and amplitude to a known correspondingslower or faster luminance response for a same or another pictureelement for an opposite change of the first video signal.
 16. A methodof video signal conversion, said method comprising: receiving a firstvideo signal corresponding to a picture element of a display device;receiving a predicted present luminance value from a memory, thepredicted present luminance value relating to a predicted presentluminance of the picture element; converting the first video signal intoa second video signal corresponding to the picture element, the secondvideo signal being based on the first video signal and the predictedpresent luminance value; determining a predicted future luminance valuerelating to a predicted future luminance of the picture element, thepredicted future luminance value being based on the first video signaland the predicted present luminance value; and storing the predictedfuture luminance value to the memory.
 17. The method of video signalconversion according to claim 16, wherein the predicted future luminancevalue relates to an expected response of the picture element to thesecond video signal.
 18. The method of video signal conversion accordingto claim 16, wherein said converting the first video signal includesapplying, as an input value to a lookup table, at least one of a valuebased on the first video signal and a value based on the predictedpresent luminance value.
 19. The method of video signal conversionaccording to claim 18, wherein said converting the first video signalincludes obtaining an output value from the lookup table, wherein thesecond video signal is based on the output value from the lookup table.20. The method of video signal conversion according to claim 18, whereinsaid determining a predicted future luminance value includes obtainingan output value from the lookup table, wherein the predicted futureluminance value is based on the output value from the lookup table. 21.The method of video signal conversion according to claim 16, said methodfurther comprising outputting the second video signal to a displaydevice, wherein the second video signal is based on a temperature of thedisplay device.
 22. The method of video signal conversion according toclaim 16, said method further comprising outputting the second videosignal to a display device, wherein the second video signal is based ona location of the picture element relative to other picture elements ofthe display device.
 23. The method of video signal conversion accordingto claim 16, wherein the second video signal has a plurality ofconsecutive changes in amplitude value with respect to the pictureelement, and wherein said converting the first video signal into thesecond video signal includes converting a first change in amplitudevalue of the first video signal into the plurality of consecutivechanges in amplitude value.
 24. The method of video signal conversionaccording to claim 16, wherein the predicted present luminance valuerelates to an expected luminance of the picture element at a time duringa first correction period, and wherein the predicted future luminancevalue relates to an expected luminance of the picture element at a timeduring a correction period subsequent to the first correction period.25. The method of video signal conversion according to claim 16, whereinsaid determining a second video signal includes adding a correctionvalue to the first video signal.
 26. The method of video signalconversion according to claim 25, wherein said correction value is basedon the first video signal.
 27. The method of video signal conversionaccording to claim 25, wherein said correction value is based on thepredicted present luminance value.
 28. The method of video signalconversion according to claim 25, said method further comprisingoutputting the second video signal to a display device, wherein saidcorrection value is based on a temperature of the display device. 29.The method of video signal conversion according to claim 25, said methodfurther comprising outputting the second video signal to a displaydevice, wherein said correction value is based on a location of thepicture element relative to other picture elements of the displaydevice.
 30. A video signal convertor comprising: a storage elementconfigured and arranged to output a predicted present luminance valuerelating to a predicted present luminance of a picture element of adisplay device; and a processing block configured and arranged toreceive a first video signal corresponding to the picture element, todetermine a second video signal corresponding to the picture element,and to determine a predicted future luminance value based on the firstvideo signal and the predicted present luminance value, wherein thesecond video signal is based on the first video signal and the predictedpresent luminance value, and wherein the storage element is furtherconfigured and arranged to store the predicted future luminance value.31. The video signal convertor according to claim 30, wherein thepredicted future luminance value relates to an expected response of thepicture element to the second video signal.
 32. The video signalconvertor of claim 30, wherein the processing block includes a lookuptable.
 33. The video signal convertor of claim 32, wherein the lookuptable is configured and arranged to receive at least one among the firstvideo signal and the predicted present luminance value as an inputvalue.
 34. The video signal convertor of claim 32, wherein the lookuptable is configured and arranged to output the second video signal as anoutput value.
 35. The video signal convertor of claim 32, wherein thelookup table is configured and arranged to output the predicted futureluminance value as an output value.
 36. The video signal convertor ofclaim 30, wherein the processing block is further configured andarranged to output the second video signal to a display device, whereinthe second video signal is based on a temperature of the display device.37. The video signal convertor of claim 30, wherein the processing blockis further configured and arranged to output the second video signal toa display device, wherein the second video signal is based on a locationof the picture element relative to other picture elements of the displaydevice.
 38. The video signal convertor of claim 30, wherein thepredicted present luminance value relates to an expected luminance ofthe picture element at a time during a first correction period, andwherein the predicted future luminance value relates to an expectedluminance of the picture element at a time during a correction periodsubsequent to the first correction period.
 39. A method of processing afirst video signal for display on a display device, the display devicehaving a picture element with different luminance response times tochanges in amplitude value of a displayed video signal that are equal inmagnitude and opposite in direction, said method comprising: receivingthe first video signal having a first change in amplitude value withrespect to the picture element, said first change being from a firstamplitude value to a second amplitude value; and determining a secondvideo signal having a second change in amplitude value with respect tothe picture element, the second change in amplitude value correspondingto the first change in amplitude value, wherein determining the secondvideo signal includes determining said second change in amplitude valuesuch that a luminance response time of the picture element to the secondchange in amplitude value is substantially equal to a luminance responsetime of the picture element to a change in amplitude value from thesecond amplitude value to the first amplitude value.
 40. The method ofprocessing a first video signal for display on a display deviceaccording to claim 39, wherein said second change in amplitude valueincludes a plurality of consecutive changes in amplitude value, saidconsecutive changes in amplitude value being separated in time.
 41. Themethod of processing a first video signal for display on a displaydevice according to claim 39 or 40, wherein the second change inamplitude value is based on an expected luminance of the pictureelement.
 42. The method of processing a first video signal for displayon a display device according to claim 41, further comprising storing apredicted future luminance value relating to an expected luminance ofthe picture element in response to the second change in amplitude value.43. The method of processing a first video signal for display on adisplay device according to claim 39, wherein the second change inamplitude value is based on the first change in amplitude value and anexpected luminance of the picture element.
 44. The method of processinga first video signal for display on a display device according to claim39, wherein determining said second change in amplitude value includesapplying, as an input value to a lookup table, at least one of a valuebased on the first change in amplitude value and a value based on anexpected luminance of the picture element.
 45. The method of processinga first video signal for display on a display device according to claim39, wherein the second change in amplitude value is based on atemperature of the display device.
 46. The method of processing a firstvideo signal for display on a display device according to claim 39,wherein the second change in amplitude value is based on a location ofthe picture element relative to other picture elements of the displaydevice.
 47. A method of processing a first video signal for display on adisplay device, the display device having a picture element withdifferent luminance response times to changes in amplitude value of adisplayed video signal that are equal in magnitude and opposite indirection, said method comprising: receiving the first video signalhaving a first change in amplitude value with respect to the pictureelement; and determining a second video signal having a second change inamplitude value with respect to the picture element, the second changein amplitude value corresponding to the first change in amplitude value,wherein determining the second video signal includes determining saidsecond change in amplitude value such that a luminance response time ofthe picture element to the second change in amplitude value is greaterthan a luminance response time of the picture element to the firstchange in amplitude value.
 48. The method of processing a first videosignal for display on a display device according to claim 47, whereinsaid second change in amplitude value includes a plurality ofconsecutive changes in amplitude value, said consecutive changes inamplitude value being separated in time.
 49. The method of processing afirst video signal for display on a display device according to claim 47or 48, wherein the second change in amplitude value is based on anexpected luminance of the picture element.
 50. The method of processinga first video signal for display on a display device according to claim49, further comprising storing a predicted future luminance valuerelating to an expected luminance of the picture element in response tothe second change in amplitude value.
 51. The method of processing afirst video signal for display on a display device according to claim47, wherein the second change in amplitude value is based on the firstchange in amplitude value and an expected luminance of the pictureelement.
 52. The method of processing a first video signal for displayon a display device according to claim 47, wherein determining saidsecond change in amplitude value includes applying, as an input value toa lookup table, at least one of a value based on the first change inamplitude value and a value based on an expected luminance of thepicture element.
 53. The method of processing a first video signal fordisplay on a display device according to claim 47, wherein the secondchange in amplitude value is based on a temperature of the displaydevice.
 54. The method of processing a first video signal for display ona display device according to claim 47, wherein the second change inamplitude value is based on a location of the picture element relativeto other picture elements of the display device.
 55. A method ofprocessing a first video signal for display on a display device, thedisplay device having a picture element with different luminanceresponse times to changes in amplitude value of a displayed video signalthat are equal in magnitude and opposite in direction, said methodcomprising: receiving the first video signal having a first change inamplitude value over a time duration with respect to the pictureelement; and determining a second video signal having a second change inamplitude value over the time duration with respect to the pictureelement, the second change in amplitude value corresponding to the firstchange in amplitude value, wherein an integrated luminance of thepicture element over the time duration in response to the second videosignal is substantially equal to the integrated luminance of a pictureelement having a predefined luminance response over the time duration inresponse to the first video signal, wherein the predefined luminanceresponse is defined as a change in luminance over time that issubstantially equal in shape and opposite in direction in response tochanges in an input video signal that are equal in magnitude andopposite in direction.
 56. The method of processing a first video signalfor display on a display device according to claim 55, wherein saidsecond change in amplitude value includes a plurality of consecutivechanges in amplitude value, said consecutive changes in amplitude valueoccurring separately during the time duration.
 57. The method ofprocessing a first video signal for display on a display deviceaccording to claim 55 or 56, wherein the second change in amplitudevalue is based on an expected luminance of the picture element.
 58. Themethod of processing a first video signal for display on a displaydevice according to claim 57, further comprising storing a predictedfuture luminance value relating to an expected luminance of the pictureelement in response to the second change in amplitude value.
 59. Themethod of processing a first video signal for display on a displaydevice according to claim 55, wherein the second change in amplitudevalue is based on the first change in amplitude value and an expectedluminance of the picture element.
 60. The method of processing a firstvideo signal for display on a display device according to claim 55,wherein determining said second change in amplitude value includesapplying, as an input value to a lookup table, at least one of a valuebased on the first change in amplitude value and a value based on anexpected luminance of the picture element.
 61. The method of processinga first video signal for display on a display device according to claim55, wherein the second change in amplitude value is based on atemperature of the display device.
 62. The method of processing a firstvideo signal for display on a display device according to claim 55,wherein the second change in amplitude value is based on a location ofthe picture element relative to other picture elements of the displaydevice.
 63. A method of video signal conversion, said method comprising:receiving a first video signal having a first change in amplitude valuewith respect to a picture element of a display device; receiving apredicted present luminance value from a memory, the predicted presentluminance value relating to a predicted present luminance of the pictureelement; determining a second video signal having a second change inamplitude value with respect to the picture element, the second changein amplitude value being based on the first change in amplitude valueand the predicted present luminance value; determining a predictedfuture luminance value relating to a predicted future luminance of thepicture element, the predicted future luminance value being based on thefirst change in amplitude value and the predicted present luminancevalue; and storing the predicted future luminance value to the memory.64. The method of video signal conversion according to claim 63, whereinthe predicted future luminance value relates to an expected response ofthe picture element to the second video signal.
 65. The method of videosignal conversion according to claim 63, wherein said determining asecond video signal includes applying, as an input value to a lookuptable, at least one of a value based on the first change in amplitudevalue and a value based on the predicted present luminance value. 66.The method of video signal conversion according to claim 65, whereinsaid determining a second video signal includes obtaining an outputvalue from the lookup table, wherein the second change in amplitudevalue is based on the output value from the lookup table.
 67. The methodof video signal conversion according to claim 65, wherein saiddetermining a predicted future luminance value includes obtaining anoutput value from the lookup table, wherein the predicted futureluminance value is based on the output value from the lookup table. 68.The method of video signal conversion according to claim 63, said methodfurther comprising outputting the second video signal to a displaydevice, wherein the second change in amplitude value is based on atemperature of the display device.
 69. The method of video signalconversion according to claim 63, said method further comprisingoutputting the second video signal to a display device, wherein thesecond change in amplitude value is based on a location of the pictureelement relative to other picture elements of the display device. 70.The method of video signal conversion according to claim 63, wherein thesecond video signal has a plurality of consecutive changes in amplitudevalue with respect to the picture element, and wherein converting thefirst video signal into the second video signal includes converting afirst change in amplitude value of the first video signal into theplurality of consecutive changes in amplitude value.
 71. The method ofvideo signal conversion according to claim 63, wherein the predictedpresent luminance value relates to an expected luminance of the pictureelement at a time during a first correction period, and wherein thepredicted future luminance value relates to an expected luminance of thepicture element at a time during a correction period subsequent to thefirst correction period.
 72. A video signal convertor comprising: astorage element configured and arranged to output a predicted presentluminance value relating to a predicted present luminance of a pictureelement of a display device; and a processing block configured andarranged to receive a first video signal having a first change inamplitude value with respect to the picture element and to determine asecond video signal having a second change in amplitude value withrespect to the picture element, wherein the first change in amplitudevalue includes a change from a first amplitude value to a secondamplitude value, and wherein the second change in amplitude value isbased on the first change in amplitude value, and wherein the processingblock is further configured and arranged to determine the second changein amplitude value based on the predicted present luminance value suchthat a luminance response time of the picture element to the secondchange in amplitude value is substantially equal to a luminance responsetime of the picture element to a change in amplitude value from thesecond amplitude value to the first amplitude value.
 73. The videosignal convertor according to claim 72, wherein the processing block isfurther configured and arranged to determine a predicted futureluminance value based on the first change in amplitude value and thepredicted present luminance value, and wherein the storage element isfurther configured and arranged to store the predicted future luminancevalue.
 74. A video signal convertor comprising: a storage elementconfigured and arranged to output a predicted present luminance valuerelating to a predicted present luminance of a picture element of adisplay device; and a processing block configured and arranged toreceive a first video signal having a first change in amplitude valuewith respect to the picture element, to determine a second video signalhaving a second change in amplitude value with respect to the pictureelement, and to determine a predicted future luminance value based onthe first change in amplitude value and the predicted present luminancevalue, wherein the first change in amplitude value includes a changefrom a first amplitude value to a second amplitude value, and whereinthe second change in amplitude value is based on the first change inamplitude value, and wherein the processing block is further configuredand arranged to determine the second change in amplitude value based onthe predicted present luminance value such that a luminance responsetime of the picture element to the second change in amplitude value isgreater than a luminance response time of the picture element to thefirst change in amplitude value, and wherein the storage element isfurther configured and arranged to store the predicted future luminancevalue.
 75. The video signal convertor according to claim 74, wherein theprocessing block is further configured and arranged to determine apredicted future luminance value based on the first change in amplitudevalue and the predicted present luminance value, and wherein the storageelement is further configured and arranged to store the predicted futureluminance value.
 76. A video signal convertor comprising: a storageelement configured and arranged to output a predicted present luminancevalue relating to a predicted present luminance of a picture element ofa display device; and a processing block configured and arranged toreceive a first video signal having a first change in amplitude valueover a time duration with respect to the picture element, to determine asecond video signal having a second change in amplitude value over thetime duration with respect to the picture element, and to determine apredicted future luminance value based on the first change in amplitudevalue and the predicted present luminance value, wherein the firstchange in amplitude value includes a change from a first amplitude valueto a second amplitude value, and wherein the second change in amplitudevalue is based on the first change in amplitude value, and wherein theprocessing block is further configured and arranged to determine thesecond change in amplitude value based on the predicted presentluminance value such that an integrated luminance of the picture elementover the time duration in response to the second video signal issubstantially equal to the integrated luminance of a picture elementhaving a predefined luminance response over the time duration inresponse to the first video signal, wherein the predefined luminanceresponse is defined as a change in luminance over time that issubstantially equal in shape and opposite in direction in response tochanges in an input video signal that are equal in magnitude andopposite in direction, and wherein the storage element is furtherconfigured and arranged to store the predicted future luminance value.77. The video signal convertor according to claim 76, wherein theprocessing block is further configured and arranged to determine apredicted future luminance value based on the first change in amplitudevalue and the predicted present luminance value, and wherein the storageelement is further configured and arranged to store the predicted futureluminance value.
 78. A method for operating a display device having apicture element with different luminance response times to changes inamplitude value of a displayed video signal that are equal in magnitudeand opposite in direction, said method comprising: receiving a firstvideo signal having video information; modifying the first video signalfrom time to time in accordance with a predetermined schedule based atleast on characteristics of the picture element to develop a secondvideo signal having the video information; and outputting the secondvideo signal to the display device, wherein said modifying includesdeveloping the second video signal such that a luminance response timeof the picture element to a value of the second video signal thatcorresponds to a first change in amplitude value of the first videosignal is substantially the same as a luminance response time of thepicture element to a value of the second video signal that correspondsto a second change in amplitude value of the first video signal, thefirst and second changes being equal in magnitude and opposite indirection.
 79. A display system comprising: a display device having apicture element with different luminance response times to changes inamplitude value of a displayed video signal that are equal in magnitudeand opposite in direction; a convertor coupled to the display device andconfigured and arranged to modify a first video signal, which has videoinformation, from time to time in accordance with a predeterminedschedule based at least on characteristics of the picture element todevelop a second video signal having the video information, wherein saidconvertor is configured and arranged to select at least one amplitudevalue of the second video signal such that a luminance response time ofthe picture element to a value of the second video signal thatcorresponds to a first change in amplitude value of the first videosignal is substantially the same as a luminance response time of thepicture element to a value of the second video signal that correspondsto a second change in amplitude value of the first video signal, thefirst and second changes being equal in magnitude and opposite indirection.